Open frame electronic chassis for enclosed modules

ABSTRACT

An open frame chassis has a top opening and a bottom opening permitting ambient airflow. A plurality of modules, each enclosing electrical components in thermal contact with a heat sink area of their corresponding module, can each be inserted in the chassis. Ambient air may flow from the bottom opening across the heat sink area of each module to the top opening to passively cool the modules and electrical components. Key pins guide the modules into place and prevent incorrect insertion of a different type of electrical module not corresponding to the electrical connection of the chassis for that slot. Guide pins on corners of the modules mate with guide holes in the chassis to secure the module to the chassis and decrease vibration. Both sides of the chassis have side openings through which the fins of the modules in the end slots of the chassis may be exposed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. 119 ofCanadian Application No. 2666014, filed on May 15, 2009, and is acontinuation of U.S. Ser. No. 12/473,558 filed on May 28, 2009 now U.S.Pat. No. 7,974,093.

FIELD OF THE INVENTION

This invention relates to modular electronic systems having a chassisand modules that are hot-swappable. More particularly, the presentinvention relates to a passively cooled modular electronic system havingan open-frame chassis permitting air flow around and through a pluralityof modules each module encasing heat generating electrical devicestherein.

BACKGROUND OF THE INVENTION

In the past, there have been many different types of modular electronicsystems having a chassis with a variety of modules that can beinterconnected to the back plane of the chassis. However, the electricalcomponents in the modules tend to generate large amounts of heat whenthey are in use. Therefore, to accommodate the heat generated by theelectrical components these conventional electronic systems generallyuse fans or other air moving means to force air flow across the modulesin order to dissipate the generated heat. However, the forced-air cooledmodular electronic systems do not operate well in harsh environments fora number of reasons. First, in harsh environmental conditions, it is notalways possible to have the fan operational and a fan failure may notbecome immediately apparent, which may cause other components to failbefore the fan failure is noticed. Second, in harsh environmentalconditions, which tend to also be dirty conditions, the air generallyhas dust and other airborne contaminants contained therein, such thatperpetually forcing air around delicate electronic components mayeventually cause undesired failures decreasing the “Mean Time BetweenFailures” (MTBF) of the modules.

To address some of the MTBF issues and provide more reliable operation,conduction-cooled enclosed chassis have been used in the past in someharsh environmental conditions. However, because conduction cooledenclosed chassis are enclosed, they are not modular and do not permitreconfiguration of the systems by the exchange of modules therein.Furthermore, such conduction cooled enclosed chassis must be entirelyreplaced even if a single component fails. As a result, such conductioncooled enclosed chassis give rise to maintenance and replacement issuesin the field, which cause Mean Time To Repair (MTTR) to decrease.

Furthermore, in addition to protecting the electrical components againstharsh environmental conditions, including dust, dirt and heat, it isalso desirable to protect the electrical devices from shock andvibration. An acute shock, or prolonged vibration, may lead to failureof highly sensitive electronic devices thereby also decreasing the meantime between failures (MTBF).

Accordingly, there is a need in the art to provide a modular electronicsystem which can operate in harsh environments without the use of aforced air cooling system. There is also a need in the art for a modularelectronic system which is resistant to environmental conditions, suchas dirt, vibration and shock to approve desired MTBF and MTTR levels.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to at least partiallyovercome some of the disadvantages of the prior art. Also, it is anobject of this invention to provide an improved type of modularelectronic system which is passively cooled.

In one aspect, the present invention provides an open frame chassishaving openings at the top, bottom and sides permitting air flow throughthe open frame chassis, to the extent possible. The chassis receivesmodules which have electrical components completely enclosed therein.The modules have a heat sink area, which in a preferred embodimentconsists of integrated fins that are in thermal contact with theelectrical components contained within the module. The modules areinserted into the open frame chassis to an inserted position and held atthe inserted position by supports. At the inserted position, a module isin electrical contact with the open frame chassis and the heat sink areaof the module is oriented between the top opening and the bottom openingof the open frame chassis. In this way, the heat sink fin area extendsvertically from the bottom opening to the top opening forming an airflow path across the heat sink area. The pressure differential built upby heat generated by the electrical components in each module andconducted through the module to the heat sink fin area builds up an airpressure differential creating convection air currents from the bottomopening through the heat sink fin areas and out the top opening of theopen frame chassis, which permits passive dissipation of the heatgenerated by the electrical components in the module.

The modules enclose different types of electrical components, such asoptical transceivers, integrated circuits, microprocessors and, for thepower module, power generation circuitry including transformers andcapacitors. The components which generate more heat are preferablymounted on the top side of the circuit card assemblies in closer contactto the heat sink fin area. Internal heat sink conductors and thermalinterface materials are used for facilitating the conduction of heataway from the electrical components and towards the heat sink fin areaof the module.

Accordingly, in one of its aspects, this invention resides in apassively cooled modular electronic system comprising: an open-framechassis having a bottom opening and a top opening permitting ambient airflow there through; a module enclosing electrical components and havinga heat sink area, said electric components in thermal contact with saidheat sink area of said module; an electrical connection on the openframe chassis for removably electrically connecting the module to theopen-frame chassis; a support for holding the module at an insertedposition where the module is in electrical contact with the electricalconnection and where the heat sink area is aligned with the bottomopening and the top opening to permit ambient air flow from the bottomopening across the heat sink area and out the top opening to passivelycool the electrical components in the module.

In a further aspect, the present invention resides in a module for usein a passively cooled modular electronics system having an open framechassis with a top opening and a bottom opening, said module comprising:a casing for enclosing electronic components therein; an electricalconnector for connecting the module to the open frame chassis; a heatsink area in thermal contact with the electrical components; wherein thecasing enclosing the electrical components is inserted into an insertedposition within the open frame chassis with the electrical connector inelectrical contact with the open frame chassis, and, the heat sink areaaligned between the top opening and the bottom opening of the open framechassis to permit ambient air flow from the bottom opening across theheat sink area and out the top opening of the open frame chassis topassively cool the electrical components in the module.

Accordingly, in one aspect, the present invention provides an open framechassis having a top opening and a bottom opening permitting ambient airflow through the open frame chassis. In this way, the chassis is notenclosed but rather hot swappable modules connected to the back plane ofthe chassis will be exposed to ambient air and convection currents canbe formed from the bottom opening to the top opening to passively coolthe electrical components enclosed in the modules. In this way, naturalconvection can be used to passively cool the electrical componentsenclosed in the module without the use of forced air cooling.Nevertheless, forced air in the form of fans may also be used if desiredor required for particular applications.

In another aspect of the present invention, the modules fully enclosetheir electrical components such that no ambient air can enter into themodules. Rather, internal conductive surfaces spread and transfer heatto the heat sink area of the module which in a preferred embodimentcomprises die cast integrated heat fins. In this way, heat generated bythe electrical devices can be directed within the modules towards theheat sink area to dissipate the generated heat in a controlled manner.Furthermore, because the modules are completely enclosed, there is noconcern of dirt or dust coming into contact with the electricalcomponents contained in the module thereby increasing the mean timebetween failures of the modules.

In a further preferred embodiment, the modules are all of the same shapeand size. This decreases the cost associated with manufacturing themodules. Preferably the modules are made of aluminium to provide amodule of reasonable weight, and also improve heat transfer abilities.It is understood that any material which is a relatively good conductorof heat would preferably be used as the casing for the modules.

In a further aspect of the invention, the modules preferably have uniquekey housing for each type of module. The key housing of the modulespreferably have key holes which mate with key pins on the back plane ofthe chassis, which key pins are oriented in different positions so thateach type of module can be connected only to the corresponding type ofchassis electrical connection in the back plane. In this way, thecorrect type of module will be inserted into the correct slot in orderto avoid damaging the electrical connections on the module and the backplane. Preferably, the key pins extend from the back plane a greaterdistance than the electrical connections, to ensure that the key pinsengage the module key housing before the electrical connections meet,thereby avoiding the possibility of damaging the electrical connectionsin the module and back plane. The key pins are also selected in the backplane such that, even if an incorrect module is inserted into the slot,the key pins will not contact the electrical connection on the module,but rather will contact a flat surface area so as not to damage anyelectrical connections on the module.

In another aspect of the invention, the modules have guide pins oralignment pins to decrease vibration and shock to the module, and moreparticularly, the electrical components contained therein. The moduleguide pins engage corresponding alignment holes in the chassis to securethe module to the chassis.

In a further aspect of the present invention, the modules have railswhich extend along the length of the module in an insertion directionand engage channels in the open frame chassis. The channels may extendacross the bottom opening and/or top opening, but are preferably narrowto avoid excess interference with the ambient air flow through the topand bottom openings. During insertion, the rail on the module engagesthe channel and is slid along the channel in an insertion directionuntil the module is at the inserted position. Preferably, the rails arelocated remotely from the heat sink area so that the channel and rail donot impede ambient air flow across the heat sink area when the module isin the inserted position. In a preferred embodiment, the heat sink areaextends along a first side wall of the module and the rail extends alongthe bottom of the module adjacent a second side wall of the moduleopposed to the first side wall.

Further aspects of the invention will become apparent upon reading thefollowing detailed description and drawings, which illustrate theinvention and preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which illustrate embodiments of the invention:

FIG. 1 is an exemplary perspective view of an open-frame modularelectronic system package supported on an open frame chassis and havingelectronic module installed thereon according to one embodiment of thepresent invention;

FIG. 2 is an exemplary depiction of the open frame chassis and backplaneof the open frame chassis of FIG. 1, but with no module installedtherein;

FIG. 3 is an exemplary front elevation view of a modular electronicssystem shown in FIG. 1 including two power supply modules (PM), onecontrol module (CM), one switch module (SM), and six communicationmodules (LM) installed in an open-frame chassis according to oneembodiment of the present invention;

FIG. 4 is an exemplary top plan view of the open-frame modularelectronic system shown in FIG. 1;

FIG. 5 is an exemplary right side view of the open-frame modularelectronic system shown in FIG. 1;

FIG. 6 is an exemplary rear perspective view of the modular electronicsystem shown in FIG. 1;

FIG. 7 is an exemplary front perspective view of a module according toone embodiment of the present invention;

FIG. 8 a is a side view of a module shown in FIG. 7;

FIG. 8 b is a bottom view of the module shown in FIG. 7;

FIG. 8 c is a rear perspective view of the module shown in FIG. 7;

FIG. 9 a is an exemplary broken-out side section view of a module,showing an internal heat conduction path according to one embodiment ofthe present invention;

FIG. 9 b is a perspective partially broken-out section view of themodule shown in FIG. 9 a.

FIG. 10 is an exemplary thermal modeling of airflow over a fin field ofeach module; and

FIG. 11 is a graphical representation showing temperature along the Yaxis and fin spacing (fin number) along the X axis representing thetemperature of the electrical components in a module according to oneembodiment of the present invention generating 10 watts of heat and 85°C. ambient temperature at different fin spacings where the fin area is100 mm by 93 mm, the fin height is 14.8 mm and the fin thickness is 1.9MM.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention and its advantages can beunderstood by referring to the present drawings. In the presentdrawings, like numerals are used for like and corresponding parts of theaccompanying drawings.

As shown in FIGS. 1 and 3 to 6, one embodiment of the present inventionprovides a passively cooled module electronic system, as shown generallyby reference numeral 10. The passively cooled modular electronic system10 comprises an open frame chassis, as shown generally by referencenumeral 100, and at least one and preferably a plurality of modules 900.While FIG. 1 shows modules in all of the slots 163 of the open framechassis, it is understood that modules 900 may only be present in someof the slots 163.

The open frame chassis 100 is better shown in FIG. 2 where all themodules 900 have been removed from the slots 163. As illustrated in FIG.2, the open frame chassis 100 comprises a bottom opening 130 and a topopening 120. It is understood that preferably the bottom opening 130 andtop opening 120 are open to the extent possible while still permittingsupport 136 to hold the modules 900 in an inserted position, whichinserted position is shown generally by reference numeral 901 in FIG. 1,in the open frame chassis 100. Having larger openings 120, 130 permitsair currents to be formed and maintained more easily. Furthermore,having larger openings 120, 130 prevents the accumulation of dirt anddust which could clog smaller openings.

The chassis 100 has a chassis cover 109 which covers the back plane 110.The back plane 110 comprises a number of electrical connections 133. Ina preferred embodiment, and discussed more fully below, the modules 900may have different types of module electrical connections 333corresponding to each type 320 of module 900. The back plane 110 hascorresponding types of chassis electrical connections 133 correspondingto each type of module electrical connection 333 to be inserted into theopen frame chassis 100. As illustrated in FIG. 3, the types of chassiselectrical connections 133 may include a power module electricalconnection 133 p, a line module electrical connection 133 l, a switchmodule electrical connection 133 s and a control module electricalconnection 133 c. Generally, the type 320 of module 900 that may beinserted into a corresponding slot 163 in the open frame chassis willcorrespond to the electrical connection 133 in the back plane 110. Toensure that one type 320 of module 900 is not inserted into a slot 163having a different type of electrical connection 133, the back plane 110comprises key pins 170 which engage corresponding key holes 380 in themodules 900.

The modules 900 also have a heat sink area, shown generally by referencenumeral 330. This heat sink area 330 facilitates dissipation of heatgenerated by the electrical components in the module 900. The electricalcomponents 902 in the module 900 are in thermal contact with the heatsink area 330 of the module 900 to facilitate transfer of heat generatedby the electric components 902 to the heat sink area 330.

As illustrated in FIGS. 9A and 9B, the modules 900 enclose electricalcomponents 902 therein. The electrical components 902 may be any type ofelectrical components 902 that can be enclosed in a module 900 and usedin a chassis 100. In FIG. 9A, the module 900 is shown as having a bottomlevel optical transceiver heat source on the daughter peripheralcomponent board (PCB) 920 and a top level optical transceiver heatsource on the main PCB 930. However, it is understood that any type ofelectrical components 902 can be contained within the module 900. Themodule 900 also has electrical connections 333 for the correspondingelectrical components 902 which mate with the chassis electricalconnections 133 to removably electrically connect the module 900 to theopen frame chassis 100.

As illustrated in FIG. 1, the supports 136 hold each of the modules 900at an inserted position 901, where the module 900 is in electricalcontact with the electrical connections 133 of the open frame chassis100, and, the heat sink area 330 is aligned with the bottom opening 130and the top opening 120 of the open frame chassis 100. This permits airto flow along the air flow path 134 from the bottom opening 130 acrossthe heat sink area 330 and out the top opening 120 to passively cool theelectrical components 902 in the module 900.

FIG. 10 shows a field of heat sink areas 330 with the corresponding airflow paths 134 passing across each of the heat sink areas 330 of aplurality of modules 900. As the heat sink areas 330 become hotter dueto the heat generated by the enclosed electrical components 902, apressure differential will be created as the hot air around the heatsink area 330 is heated, expands and rises. Additional ambient air willthen flow in to take the place of the previously heated air creating theair flow path 134 from the bottom opening 130 across the heat sink area330 and out the top opening 120. Furthermore, the modules 900 havingcomponents 902 which generate more heat and will generate more of apressure differential thereby drawing additional air flow 134 across theheat sink area 330 to the hotter modules 900. In this way, the passivelycooled modular system 10 is self regulating in that the modules 900having components 902 that generate more heat will correspondinglygenerate further air flow to further facilitate heat dissipation.

As illustrated in the figures, in a preferred embodiment the heat sinkarea 330 comprises a heat sink fin area 332 having a plurality of fins331. The fins 331 preferably extend along the vertical axis VA shown inFIG. 1 when the modules 900 are in the inserted position 901. In thisway, heat generated by the electrical devices 902 and conducted to theheat sink fin area 332 will facilitate the heating and rising of airacross the heat sink area 330. Accordingly, it is understood thatpreferably the open frame chassis 100 is oriented such that the heatsink fin areas 332 are oriented vertically, however it is understoodthat other orientations are still operable, but may be less efficient.It is also preferred that there is spacing between the top and bottomopenings 120, 130 of the open frame chassis 100 and other elements (notshown) in the rack (not shown) in order to permit ambient air flow. Thisspacing preferably 1.75 inches or more.

In a preferred embodiment, where the heat sink area 330 comprises a heatsink fin area 332 having a plurality of fins 331, the fins 331 areseparated by a distance of between 6 mm and 14 mm. More preferably, thefins 331 are separated by a distance of between 9 mm and 12 mm and havea height of 14 mm to 20 mm. This preferred orientation and sizing hasbeen determined based on modelling as illustrated in FIG. 11. Inparticular, FIG. 11 is a graphic presentation showing the temperaturealong axis Y in degrees Celsius and the fin spacing, as well as finnumber in brackets along the X axis. The model illustrated in FIG. 11 isbased on a module 900 as shown in FIG. 8 a to FIG. 8 c in an ambienttemperature environment of 85° C. and having electrical components 902generating 10 watts of heat. The heat sink fin area 332 is presumed tobe constant at 100 mm by 93 mm and the height is considered to be 14.8mm and the fin thickness is 1.9 mm. It is understood that while thenumber of fins 331 increase, the fin spacing decreases because the finarea 332 remains constant. Therefore, there is a balance between thenumber of fins 331 possible in the heat sink area 330 and the spacingbetween the fins 331. As shown in FIG. 1, the temperature decreasesnoticeably when the fins 331 are separated by a distance of 6 mm and 14mm. More preferably, there is a further noticeable drop in temperaturewhen the fins 331 are separated by a distance of between 9 mm and 12 mm.This is particularly true in the present case where the height of thefins is 14.8 mm, but would also be the case if the fin height extendedup to 20 mm assuming the spacing of the modules 900 in the open framechassis 100 and the orientation of the components 902 in the module 900permitted this height of fins 331.

In addition to the top and bottom openings 120, 130, the open framechassis 100 also preferably comprises a left side opening 151 and aright side opening 152 as shown, for instance, in FIGS. 5 and 6. Thispermits added ambient air flow across the module 900 inserted into theend slots 164, 165 through the side openings 151, 152. Because of this,it is preferred that modules 900 which tend to generate the most heatwill be placed at the end slots 164, 165. Because the power module 320 ptends to generate the most heat, it is preferred if the end slots 164,165 have power module electrical connections 133 p. In this way, thepower modules 320 p, which tend to generate the most heat, will have theadded benefit of air flow from the left side opening 151 and the rightside opening 152 across the heat sink area 330.

FIG. 3 illustrates the different types of modules 320 p, l, s, c whichare also identified by their two letter codes. For instance, as shown inFIG. 3, the end slots 164, 165 have power modules (PM) 320(p) insertedtherein. As discussed above, this is preferred because the power modulesPM 320 (p) generate the most heat and the open frame chassis 100 hasside openings 151, 152. As is also apparent from FIG. 3, the powermodules PM 320(p) are reversed for reasons which will be discussed morefully below. The other modules shown in FIG. 3 include the line modules(LM) 320(l), the switch module (SM) 320(s) and the control module (CM)320(c) which performs different functions. It is appreciated that theelectrical components 902 in each of the modules 900 will performspecific functions in the network.

Each of the modules 900 preferably have external connections on theirfront input/output side 312. These electrical connections include fiberoptic connections 401, RJ 45 connections 402 and D-subminiatureconnection 403. It is understood however that any type of connectionsmay be present on the input/output side 312 of the modules 900.

Each of the modules 900 also have panel mount screws 314. The panelmount screws engage holes on the open frame chassis 100 to urge themodules 900 towards the back plane 110 of the chassis 100. The modules900 may also have handles 322 for lifting and moving the modules 900. Itis understood that if the modules 900 have a metal casing 903, which maybe relatively heavy and the module handles 322 facilitate movement ofthe module 900.

As indicated above, the chassis 100 will have different electricalconnections 133, p, l, s, and c for connecting to a correspondingdifferent type 320 of module 900. The different types 320 p, l, s, c ofmodules 900 will connect to a corresponding chassis electricalconnection 133 p, l, s, c and the support 136 will be present for eachof the types 320 p, l, s, c of the modules 900 at the inserted position901 where the heat sink area 330 is aligned with the bottom opening 130and the top opening 120. In this inserted position 901, the air flowpath 134 permits air to flow from the bottom opening 130 across the heatsink area 330 of each of the modules 900 and out the top opening 120 topassively cool the electrical components 902 in each of the modules 900.

To prevent incorrect insertion of a different type of module 900 with anon-corresponding type of chassis electrical connection 133, the system10 comprises key pins 170 associated with each type of electricalconnection 133 p, l, s and c. Each of the key pins 170 have a uniqueorientation for each type of chassis electrical connection 133 p, l, s,c and mate with the corresponding key holes 380, shown for instance inFIGS. 8 a to 8 c, on the module key housing 336 of each type 320 p, l,s, c of module 900. As is apparent for instance from FIG. 2, the keyguides 170 will be at a different location in the back plane 110corresponding to the type of electrical connection 133 p, l, s, c. Inthis way, if the incorrect type 320 p, l, s, c of module 900 is insertedinto one of the slots 163, the key pins 170 will not mate with thecorresponding key holes 380 on the module key housing 336 of the module900 thereby prevent the full insertion of the module 900 completely intothe inserted position 901 of the slot 165. Preferably, the key guides170 are longer than the chassis electrical connections 133. In this way,the key guides 170 will contact the module 900 before the chassiselectrical connections 133 contact the key housing 336 of the incorrectmodule electrical connections 333 which could avoid or lessen anypotential damage resulting from incorrectly inserting a type 320 ofmodule 900 into slot 165 with a chassis electrical connection 133 p, l,s, c which does not correspond to the type of module electricalconnector 333 for that type 320 p, l, s, c of module 900.

Modules also preferably comprise module guide alignment pins 370,illustrated for instance in FIG. 8 a to FIG. 8 c. These module guidealignment pins 370 mate with corresponding alignment holes 180 (shown inFIG. 2) in the back plane 110 of the chassis 100 to decrease vibrationand avoid shocks between the module 900 and the open frame chassis 100.Preferably, the module guide alignment pins 370 are located at the fourcorners of each module 900 as illustrated for instance in FIG. 8 c andFIG. 9 b. It is understood that having the module guide alignment pins370 as far apart as possible and at the corners of the module 900 willimprove resistance to external forces including rotational andvibrational forces. While additional module guide alignment pins 370 maybe used, it has been found that having four module guide alignment pins370 at the corners of the module provide adequate suppression ofvibration and shock.

In a preferred embodiment, as illustrated in FIGS. 1 and 2, the support136 comprises channels 160 in the chassis 100. At least one bottomchannel 162 is present for each slot 165. The bottom channel 162 extendsacross the bottom opening 130 and is designed to minimally affect thesize of the bottom opening 130 and the air flow paths 134 therethrough.In a preferred embodiment, top channels 161 are also provided across thetop opening 120 for each of the slots 165. Preferably the top channels161 are aligned with the bottom channels 161 along the vertical axis VAto minimally affect the air flow paths 134 which are also generallyaligned with the vertical axis VA.

The modules 900 have at least one rail 360 for engaging the bottomchannel 162 and, in a preferred embodiment, if present, a top rail 361for engaging the top channel 161. During insertion, the modules 900 areinserted in the insertion direction ID as shown, for instance, inFIG. 1. The bottom rail 360 engage the bottom channel 160 while themodule 900 is inserted in the insertion direction ID to the insertedposition 901 where the heat sink area 330 is aligned with the bottomopening 130 and the top opening 120 to permit ambient air flow 134 fromthe bottom opening 130 across the heat sink area 330 and out the topopening 120 to passively cool the electrical components 902 in themodule 900. If a top channel 101 is present, in a preferred embodiment,the top rail 361 will engage the top channel 161 while the module 900 isinserted in the inserted direction ID.

As illustrated in FIG. 7, the rails 360, 361 extend in the insertiondirection ID along the module 900. In a preferred embodiment, the rails360, 361 are located remotely from the heat sink area 330 in the module900. This is in part so that the channel 160, which engages the bottomrail 360, is located remotely from the heat sink area 330 so as not togreatly affect the air flow path 134 around the heat sink area 330. In apreferred embodiment, as illustrated in FIGS. 8A to 8C, the heat sinkarea 330 is located on a first side wall 391 of the casing 903 and therails 360 are located on the second side wall 392 which is opposed tothe first side wall 391. In this way, the rails 360 and the channels 160will be located remotely from the heat sink area 330 to lessen theirinterference with the air flow paths 134.

As best illustrated in FIG. 4, the chassis 100 comprises a reversechannel 160 r. The reverse channel 160 r permits a module 900 to beinserted in a reverse orientation. As illustrated, for instance in FIG.4, the heat sink area 330 of each of the modules 900 face to the right,except for the module 900 inserted in the end slot 164. This is designedto permit the heat sink area 330 of the module 900 inserted in the endslot 164 to face the left side opening 151 to increase the air flow 134across the heat sink area 330. As also illustrated in FIG. 2, thechassis electrical connections 133 p at the end slots 164, 165 arereversed. In this way, even though the power modules 320 p PM aresubstantially identical externally, they can be connected at either endslot 164, 165 and still have the heat sink area 330 face out thecorresponding side openings 151, 152 as illustrated in FIGS. 5 and 6.This is the case even if the power modules PM 320 p are substantiallyidentical externally, including the key housing 336, which decreases thecost of manufacture and also decreases the number of power modules PM320 p that must be purchased by the user because the power module 320 pin the end slot 164 will be in a reverse orientation at the insertedposition 901.

In a further preferred embodiment, all of the modules 900 have the sameexternal casing. This decreases the cost of manufacture of each of themodules 900 by requiring only a single form to create the case 903.Furthermore, this decreases the cost of maintenance of the modules 900by permitting the same casing 903 to be used to enclose various types ofelectrical components 902.

Furthermore, it is preferred that the casing 902 be made of a thermallyconductive material in order to permit conduction of heat from theelectrical components 902 to the heat sink area 330. In a preferredembodiment, the casing 903 is made from a variety of thermallyconductive materials including, but not limited to, aluminium andaluminium alloys. In a preferred embodiment, the casing 903 ismanufactured using aluminium alloy die casting. As indicated above, allof the modules 900 are preferably exactly the same having a universalenclosure 903 excluding the key housing 336. The open frame chassis 100may be formed of adequately rigid materials such as, but not limited to,metals including aluminium alloys, but also including polymers, ceramicsand composite materials. While preferred, the material used tomanufacture the open frame chassis 100 need not be thermally conductive.However, the materials used to manufacture the open frame chassis 100should have sufficient rigidity to permit several openings 120, 130,151, 152 to permit the air flow paths 134 to form.

FIGS. 9A and 9B illustrate the internal heat conduction path of themodules 900. As illustrated in FIGS. 9A and 9B, in this embodiment, theelectrical components 902 comprise bottom level optical transceiver heatsources 920 on the daughter PCB 990 and top level optical transceiverheat sources 930 on the main PCB 980. A thermal interface material 970decreases the contact thermal resistance between the bottom leveloptical transceiver 920 and the module enclosure front portion 950. Themodule enclosure front portion 950 may act as a heat sink, even thoughit does not have fins 331 and also may act as a heat spreader orconductor conducting heat to the heat sink area 330.

In a preferred embodiment, as illustrated in FIGS. 9A and 9B, the heatsink area 330 comprises a modular integrated heat sink fin area 940which is integrally formed with the overall module casing 903. Inparticular, the module enclosure front portion 950 and the moduleintegrated heat sink fin area 940 are manufactured from the sameintegrated component to facilitate the transfer of heat from the bottomlevel transceiver 920 to the heat sink area 940.

Furthermore, the module 900 comprises a module PCB clamp bar 960 locatedintermediate and in thermal contact with the top level opticaltransceiver heat source 930 on the main PCB 980 and the casing 903. Inparticular, the module PCB clamp bar 960 is in thermal contact with thesecond wall 392 of the module 900 which, in turn, is in thermal contactwith the first wall 391 where the heat sink area 330 is located, and ina preferred embodiment into which the integrated heat sink fin area 940,are formed. In this way, the PCB clamp bar 960 facilitates transfer ofheat from the top level optical transceiver 930 and the main PCB 980 tothe second wall 392 and the integrated heat sink area 940.

Furthermore, the module 900 comprises an internal heat sink 910. Theinternal heat sink 910 acts as a heat spreader or a conductor of heatfrom both the main PCB 980 and the daughter PCB 990 to the heat sinkarea 330. More particularly, the general heat sink 910 transfers heatfrom the bottom level optical transceiver 920 and the top level opticaltransceiver 930 to the heat sink area 330 which, in a preferredembodiment, comprises the integrated heat sink fin area 940.Accordingly, the internal heat spreader 910 is enclosed within themodule casing 903 and in thermal contact with the electrical components902 and facilitates transfer of heat generated by the internalcomponents 902 to the heat sink area 940 internally of the module 900.To further facilitate the transfer of heat from the internal heatspreader 910 to the integrated heat sink fin area 940, the internal heatspreader is fastened to the heat sink area 330, which in this preferredembodiment comprises the integrated heat sink area 940, using thermallyconductive fasteners 972 to facilitate the transfer of heat from theinternal heat spreader 910 to the integrated heat sink area 940. Thethermally conductive fasteners 972 may be manufactured from anyconductive materials including aluminium, aluminium alloys, steel, ironand various metals and metal alloys.

It is also understood that the entire casing 903 may be used to transferheat generated by the electrical components 902 to the heat sink area940 to passively dissipate heat to the ambient air. Furthermore, thecasing 903 will also assist in transferring heat to the ambient air evenin portions which do hot have fins 331, such as the module front portion950 as well as the second wall 392.

As also illustrated in FIGS. 9A and 9B, the module guide alignment pins370 are preferably formed with the casing 903. In this way, vibrationand shock can be lessened. Furthermore, the internal heat spreader 910,because it is located internally of the module 900 and between the mainPCB 980 and the daughter PCB 990, further facilitate dampening ofvibrations within the module 900. In addition, the module PCB clamp bar960 is selected such that the main PCB 980 and the daughter PCB 990 aresnugly fit within the module 900. This decreases the vibration and shockto the components 902. Furthermore, this also increases the pressureapplied between the various electrical components 902 and the thermallyconductive components, such as the module enclosure front portion 950through the thermal interface material 970 on the bottom level opticaltransceiver 920 to decrease thermal contact resistance and increase thethermal conduction of heat from the bottom level optical transceiver920, or other electrical or optical components 902, to the heat sinkarea 330 which, in this preferred embodiment, comprises the integratedheat sink fin area 940.

Accordingly, in operation, the modules 900 may be “hot swappable” intoand out of the open frame chassis 100. The modules 900 can be insertedby pushing them in the insertion direction ID into the correspondingslot 165 having electrical connections 133 which are appropriate for thetype 320 of module 900 and also can mate with the module electricalconnections 333. If an attempt is made to insert a type 320 of module900 having the module electrical connectors 333 which do not correspondto the chassis electrical connectors 133, the key pins 170 on the backplane 110 will not mate with corresponding module key holes 380, butrather will contact the module key housing 336 preventing insertion ofthe incorrect module into the inserted position 901. Rather, when thecorrect type 320 of module 900 for the corresponding slot 163 isinserted in the insertion direction ID, the key pins 170 in the backplane 110 will mate with the module key holes 380 permitting theinsertion of the module 900 in the insertion direction ID to theinsertion position 901. In the inserted position 901, the chassiselectrical connection 133 on the open frame chassis 100 will removablyelectrically connect the module 900 to the electrical components of theopen frame chassis 100. The support 136, which in a preferred embodimentcomprises the channels 160, will hold the module 900 at the insertedposition 901 where the module 900 is in electrical contact with thechassis electrical connection 133 and where the heat sink area 330 isaligned with the bottom opening 130 and the top opening 120 of the openframe chassis 100 to permit ambient air flow from the bottom opening 130across the heat sink area 330 and out the top opening 120 to passivelycool the electrical components 902 in the module 900.

As discussed above, the module 900 encloses electrical components 902and has a heat sink area 330 with the electrical components 902 inthermal contact with the heat sink area 330 of the module 900. Thecasing 903 of the modules 900 are preferably all the same orsubstantially the same external construction to decrease manufacturingcosts and improve ease of use of the module 900. Furthermore, the moduleguide alignment pins 370 mate with corresponding alignment holes on thechassis 180 to decrease vibration and shock to the module 900 and alsoassist in finally aligning the module 900 and, in particular, the moduleconnectors 333 to the chassis electrical connectors 133. The panel mountscrews 314 are screwed into the open frame chassis 100 adding additionalbiasing force on the modules 900 in the insertion direction ID tofacilitate a connection between the chassis electrical connections 133and the module electrical connectors 333, as well as engagement of themodule guide alignment pins 370 and the alignment holes 180 on thechassis 100.

It is understood that the invention has been described in terms of asystem including the open frame chassis 100 and the modules 900 toprovide passive cooling of the module electronic system 10.Nevertheless, a fan module (not shown) or other forced air system (notshown) may also be used to facilitate the circulation of air across themodules 900 and, in particular, the fin area 340. Moreover, having theelectrical components 902 contained within the modules 902 prevents dirtand dust from coming into contact with the electrical components 902thereby providing an advantage even if a forced air device (not shown)is used. Furthermore, the fact that large openings 130, 120, as well asside openings 151, 152 are present in the open frame chassis 100,decreases the likelihood that these openings 120, 130, 151 and 152 willbecome clogged with dust or dirt even if a forced air system (not shown)is continuously used. Furthermore, the modules 900 preferably completelyenclose the electrical component 902 and protects them from the fansystem (not shown) forcing air having entrained therein dust and dirtwhich are inherent in harsh environments. Accordingly, while the presentsystem 10 has been designed to passively cool the electrical components902 in the modules 900, this does not preclude the use of a forced airsystem (not shown) with the passively cooled module electronic system 10of the present invention.

It is also understood that while the invention has been described withrespect to optical transceiver 920, 930, the invention is not limited tothese types of electrical components 902. Rather, the invention can beused with any type of electrical components 902. Furthermore, in thiscontext, electrical components 902 includes electro-optical componentsand optical components which may generate light, such as laser light,for use with fiber optics and/or optical computer systems.

To the extent that a patentee may act as its own lexicographer underapplicable law, it is hereby further directed that all words appearingin the claims section, except for the above defined words, shall take ontheir ordinary, plain and accustomed meanings (as generally evidenced,inter alia, by dictionaries and/or technical lexicons), and shall not beconsidered to be specially defined in this specification.Notwithstanding this limitation on the inference of “specialdefinitions,” the specification may be used to evidence the appropriate,ordinary, plain and accustomed meanings (as generally evidenced, interalia, by dictionaries and/or technical lexicons), in the situation wherea word or term used in the claims has more than one pre-establishedmeaning and the specification is helpful in choosing between thealternatives.

It will be understood that, although various features of the inventionhave been described with respect to one or another of the embodiments ofthe invention, the various features and embodiments of the invention maybe combined or used in conjunction with other features and embodimentsof the invention as described and illustrated herein.

Although this disclosure has described and illustrated certain preferredembodiments of the invention, it is to be understood that the inventionis not restricted to these particular embodiments. Rather, the inventionincludes all embodiments, which are functional, electrical or mechanicalequivalents of the specific embodiments and features that have beendescribed and illustrated herein.

What is claimed is:
 1. A passively cooled modular electronic systemcomprising: an open frame chassis; a plurality of enclosed modules, eachmodule enclosing electrical components; a plurality of chassiselectrical connections on the open frame chassis for removablyelectrically connecting the plurality of modules to the open framechassis; a support for holding each module at the inserted positionwhere each module is in electrical contact with one of the plurality ofelectrical connections; wherein the plurality of modules are selectedfrom two or more types of modules, each type of module having differentelectrical components enclosed therein and a different module electricalconnection for connecting that type of module to a corresponding type ofchassis electrical connection; and wherein the open frame chassiscomprises key pins associated with each type of chassis electricalconnection, the key pins having an orientation on the open frame chassisunique to each type of chassis electrical connection, the key pinsmating with corresponding key holes in the type of module whichcorresponds to that type of chassis electrical connection.
 2. Thepassively cooled modular electronic system as defined in claim 1 whereinthe open frame chassis has openings permitting air flow therethrough tocool the modules.
 3. The passively cooled modular electronic system asrecited in claim 2 wherein each enclosed module has a heat sink area inthermal contact with enclosed electrical components.
 4. The passivelycooled modular electronic system as defined in claim 3 wherein, wheneach module is in the inserted position, air may flow through theopenings of the open frame chassis and across the heat sink area of eachmodule.
 5. The passively cooled modular electronic system as defined inclaim 4 wherein the openings of the open frame chassis comprise a bottomopening and a top opening permitting ambient air flow through.
 6. Thepassively cooled modular electronic system as defined in claim 5wherein, when in the inserted position, the heat sink area of eachmodule is aligned with the bottom opening and the top opening; andwherein ambient air is permitted to flow from the bottom opening acrossthe heat sink areas and out the top opening to passively cool theelectrical components in the modules.
 7. The passively cooled modularelectronic system as defined in claim 1 wherein the heat sink areacomprises a heat sink fin area having a plurality of fins extendingalong a vertical axis intersecting the bottom opening and the topopening.
 8. The passively cooled modular electronic system as defined inclaim 7 wherein the fins are separated by a distance of between 9 mm and12 mm and have a height of 14 mm to 20 mm.
 9. The passively cooledmodular electric system as defined in claim 1 wherein the key pinscontact the module before the module electrical connection contacts thechassis electrical connection to prevent contact of one type of moduleelectrical connection with a different type of chassis electricalconnection.
 10. The passively cooled modular electronic system asdefined in claim 1 wherein each module comprises two or more moduleguide alignment pins engaging alignment holes on the open frame chassisfor securing the module to the open frame chassis to at least one ofassist with final module alignment and decrease susceptibility of themodule and the electrical components contained therein to at least oneof shock, vibration, and rotational forces.
 11. The passively cooledmodular electronic system as defined in claim 9 wherein each modulecomprises two or more module guide alignment pins engaging guide pinholes on the open frame chassis for securing the module to the openframe chassis; wherein the guide alignment pins are located on each ofthe modules and intersect guide holes on the back plane; wherein the keypins are located on the back plane and intersect keyholes on themodules; and wherein the key pins extend a greater distance from theback plane than the guide pins extend from the module.
 12. The passivelycooled modular electronic system as defined in claim 9 wherein the typesof modules are selected from control modules CM, power supply modulesPM, switch modules SM and communication line modules LM.
 13. Thepassively cooled modular electronic system as defined in claim 1 whereinthe support for holding each module comprises: at least one channelextending in an insertion direction across the bottom opening; at leastone rail associated with each module for engaging the at least onechannel; and wherein during insertion, the at least one rail engages theat least one channel and permits the module to move in the insertiondirection to the inserted position if the key pins on the open framechassis can mate with the key holes in the type of module beinginserted.
 14. The passively cooled modular electric system as defined inclaim 9 wherein each type of module has a substantially identicalcasing.
 15. The passively cooled electronic system as defined in claim 2wherein the back plane of the open frame chassis terminates at first andsecond ends of the open frame chassis, and the openings comprise a firstopening at the first end and a second opening at the second end; whereinthe plurality of modules includes power modules (PM) and each powermodule PM has a substantially identical casing; wherein a first powermodule can be placed at the first end of the open frame chassis with theheat sink area of the first power module exposed at least partiallythrough the first opening at the first end of the open frame chassis;and wherein a second power module can be placed at the second end of theopen frame chassis such that the heat sink area of the second powermodule is exposed at least partially through the second opening of thesecond end of the open frame chassis.
 16. The passively cooled modularelectronic system as defined in claim 1 wherein the module furthercomprises: an internal heat spreader encased within the module and inthermal contact with the electrical components and the heat sink area totransfer heat generated from the electrical components to the heat sinkarea internally of the module.
 17. The passively cooled modularelectronic system as defined in claim 1 wherein the module enclosing theelectrical components comprises: a main Peripheral Circuit Board (PCB)containing the electrical components; and a PCB clamp bar in thermalcontact with the PCB and the heat sink area to transfer heat generatedfrom the electrical components to the heat sink area.
 18. The passivelycooled modular electronic system as defined in claim 16 furthercomprising thermally conductive fasteners to fasten the internal heatspreader to the heat sink area and facilitate transfer of heat from theinternal heat spreader to the heat sink area; and wherein the modulecomprises a thermally conductive casing to transfer heat generated fromthe electrical components to the heat sink area and to passivelydissipate heat to the ambient air.
 19. The passively cooled modularelectronics system as defined in claim 1 wherein at least one modulecomprises: a casing for completely enclosing electronic componentstherein; an electrical connector for connecting the module to the openframe chassis; and a heat sink area in thermal contact with theelectrical components.
 20. The passively cooled modular electronicsystem as defined in claim 19 wherein the at least one module furthercomprises: at least one rail on the casing located remotely from theheat sink area and extending along the casing in an insertion direction;and wherein, during insertion of the module into the open frame chassisin the insertion direction, the at least one rail engages at least onecorresponding channel in the open frame chassis to support the module atthe inserted position.
 21. The passively cooled modular electronicsystem as defined in claim 19 wherein the at least one module furthercomprises: an internal heat spreader in thermal contact with theelectrical components to transfer heat generated by the electricalcomponents to the heat sink area internally of the module.
 22. Thepassively cooled modular electronic system as defined in claim 19wherein the heat sink area of the at least one module comprises: a heatsink fin area having a plurality of fins extending along a vertical axisintersecting the top opening and the bottom opening of the open framechassis, the fins separated by a distance of 6 mm and 14 mm and having aheight of 14 mm to 20 mm.